Synergistic interplay of ionic liquid and dodecyl sulphate driving the oxidation state of polypyrrole based electrodes

Abstract

Herein, polypyrrole (PPy) films are prepared via electrochemical deposition in a mixture of 1-n-butyl-3-methylimidazolium methanesulfonate (BMI·CH₃SO₃) ionic liquid (IL) and dodecyl sulfate (DS). The physico-chemical properties of the films have been investigated by a wide range of characterization techniques. PPy films synthesized in DS or IL have shown larger and irregular granules as compared to PPy films prepared in the mixture of DS and IL. This result is related to the preferential dissolution of pyrrole monomers in micelle templates formed by the IL and a co-assembly of IL and dodecyl-sulfate (DS), thereby decreasing the granule size and affecting the structural arrangement of the polymer chain. The template behavior of the IL in combination with DS promotes the selective formation of polaron and bipolaron states in the PPy films. This effect has been investigated by UV-Vis spectrophotometry, Raman spectroscopy, electrochemical impedance spectroscopy (EIS), cyclic voltammetry, scanning electron microscopy, transmission electron microscopy, and electrical conductivity measurements. The synergy of IL–DS has helped to decrease the resistivity of the PPy film from 2.17 × 10² Ω cm for PPy–IL to 2.44 Ω for PPy–IL–DS. EIS has also shown a decreased interfacial charge transfer resistance for PPy–IL–DS when compared to PPy–IL. The cyclic voltammetry curves have shown that the PPy films are electrocatalytically active for the I⁻/I₃⁻ redox reaction, and therefore, can be applied as a counter electrode (CE) in dye sensitised solar cells. The PPy based CEs resulted in nearly the same photocurrent and energy conversion efficiencies as that obtained from a conventional Pt CE.